Fishing, In Oil and Gas, is a process of recovering or removing lost, damaged, stuck or unwanted material from the wellbore. This unwanted, undesirable or lost material in the wellbore is termed a fish – In the oil and gas industry, a fish is defined as any undesirable piece of equipment that is found or stuck in the wellbore and that can prevent operational activities. In other words, the removal of a fish from the wellbore is known as fishing.
Having undesirable materials (a fish) in the wellbore can halt drilling or completion processes thereby preventing operational processes. Like they say, time is money and this means that when a fish is noticed, an attempt to remove it to restore back operations is immediately initiated, that is, fishing operations.
What could possible lead to having a fish in a wellbore in oil and gas? Let us see them now.
Situations that Require Fishing Operations In Oil and Gas
Tools and equipment can be lost in the wellbore for a number of reasons or situations. Some of the situations requiring fishing operations to be carried out are:
- Twist off of the drill string – a twist off occurs when a stuck drill pipe is still being rotated in the wellbore until the pipe essentially shears off.
- Items falling from the surface (rig floor) downhole.
- Differential sticking – This is a situation in which a part of the drill stem gets stuck to the wall of the wellbore. This happens when the overbalance pressure in the wellbore pushes the drill stem against the side of the wellbore.
- Key seating – Imagine your wellbore has a groove worn on the side (like a keyhole) and tool joints of your string happens to sit on the hole. A keyseat would be formed and your string would be trapped. If the drill string is pulled continually in the process of freeing stuck pipe, it might shear and fishing operations would be required.
- Wireline logging tools can get stuck too during the process of carrying out Logging while drilling (LWD) etcetera.
There are lots of other situations that may lead to a fish in a wellbore and in such situations, knowing the right fishing tool to use and technique to employ is very necessary. Take note that during fishing operations, if adequate care is not taken, your fishing tool might become a fish itself.
Common Fishing Tools used in Fishing Operations in Oil and Gas
The following are some of the common tools employed in fishing in oil and gas. They are designed to recover equipment lost in a well and they are:
In a situation where a fish has been noticed downhole and it has begun to hinder operational activities, you should first identify the fish, it’s shape, size, configuration, etc. This is done so as to determine the best and cost-effective fishing tool to run down for retrieval or removal. This can be easily done by sending down a fishing tool known as the impression block. It is a tool sent downhole simply to identify or give an impression of the fish downhole. After identification of the fish, the appropriate fishing tools can now be employed.
As you may have already guessed, a magnet can be sent downhole to retrieve small pieces of metal from the wellbore.
In oil and gas, a junk basket is a fishing tool or device made up to the bottom of a fishing string to collect and retrieve junk pieces from the bottom of the wellbore. There are several types of junk baskets – core-type junk basket, finger-type junk basket, hydrostatic-junk basket, jet-powered junk basket. They basically carry out the same function just with different mode of operation.
A fishing jar is a mechanical device that is operated mechanically to deliver an upward thrust to a stuck pipe (fish). The upward thrust is delivered by the sudden release of a tripping device in the jar. Most often, a jar is used alongside a jar accelerator which increases the intensity of the repeated upward blows until a stuck pipe is successfully fished out. A jarring setup for fishing in oil and gas would be a catching tool, jar or jars, drill collars, and drill string.
In most cases before a fish can be retrieved, it has to be prepared. For instance, after running the impression block downhole and the fish was observed to have an uneven surface, the surface of the fish has to be made even for retrieval using a tungsten carbide flat mill. Also, in a situation where the fish needs to be drilled into, a tapered mill can be employed before retrieval. Note that the mills are made of tungsten carbide and can dress off the fish to its desired shape for retrieval.
A washover pipe is a fishing accessory that is used in fishing operations to go over the outside wall of a stuck pipe in a wellbore. The washover pipe consists of a casing and a shoe. It essentially washes away cuttings, mud, filter cake, debris etcetera, that may have gotten the pipe stuck in the first place. It cleans the annular space surrounding the stuck pipe and allows recovery of the pipe mostly in situations like key-seating and differentially stuck pipe. It is sometimes known as washpipe.
This happens to be the most commonly used equipment in fishing operations. An overshot is a fishing tool with a large diameter, that is lowered over the outside wall of a stuck pipe or any similar fish lost or stuck in the wellbore. As soon as the overshot “swallows” the fish, its internal mechanism (slips) allows for an extremely firm grip on the outside of the fish. This allows the retrieval of the fish from the wellbore.
A pipe spear is a fishing tool that is designed to enter an opening in the fish and grip its Internal Diameter to enable recovery.
The wireline spear is custom designed for fishing wireline from the wellbore. It is fitted with prongs to catch broken wireline and retrieve it to the surface.
Now that we know the common fishing tools, there is also the need to understand that some fishing jobs can go on for months. And the longer the fishing period becomes, the higher the lost drilling time and the cost of fishing operations may begin to seem like an economic fail. So in general, if the lost equipment or tool happens to be of high replacement value and the cost of production can easily offset cost of fishing then fishing operations in oil and gas can be left to linger on.
If the reverse is the case and the replacement value is low and the fish can easily be replaced, then fishing operations should be abandoned. Instead re-drilling or sidetracking (simply drilling around downhole fish) can be carried out.
Precautions to Take to Avoid Having a Fish in a Wellbore
To prevent the occurrence of a fish downhole and to Completely avoid fishing operations, the following precautions must be adhered to with all severity:
- Follow onsite precautions and ensure no equipment drops downhole through the rig floor.
- The drilling torque should be monitored carefully to avoid twist off.
- Under-gauged holes or carrot holes should be renamed out as early as noticed.
- Inspect all components of the drill string and Bottom Hole Assembly before drilling operations commence.
- Whenever necessary, carry out a full viscous sweep to remove excess drill cuttings downhole.
- Carefully inspect fishing tools before use as failure to do this might lead to your fishing tool becoming a fish etcetera.
There you have it! The question, what is fishing in oil and gas has been answered duly and the common fishing tools used in fishing in oil and gas have been highlighted as well. Please leave your questions in the comment section and share!